FIG. 22 is a schematic diagram showing an example of a commercial offset type rotary printing machine that is one of the rotary printing machines, FIG. 23 is a schematic diagram showing an example of a folding machine (comprising a web cutting unit and a paper discharger) adopted in the commercial offset type rotary printing machine, and FIG. 24 is a schematic diagram for explaining an example of the catching-folding unit of the folding machine.
As shown in FIG. 22, an ordinary commercial offset type rotary printing machine comprises eight major parts: a paper feeder part 1; an infeed part 2; a printing part 3; a drying part 4; a cooling part 5; a web passing part 6; a folding machine 7; and a paper discharger part 8 for discharging a sheet folded in the folding machine 7 outside the machine. In the paper feeder part 1, a new web roll 1b is waiting for being used next to a web roll 1a being used. The printing part 3 is equipped with a number of printing units that corresponds to the number of print colors. In this example, it is equipped with four printing units 3a to 3d. 
As shown in FIG. 23, the folding machine 7 and paper discharger part 8 comprise a drag roller 11, a triangular plate 12, a pair of lead-in rollers 13a and 13b, a pair of nipping rollers 14a and 14b, a web cutting unit 20, an accelerating belt conveyor 30, a catching-folding unit 40B, a paper discharge belt conveyor 46, a sheet alignment stacker 80 (see FIG. 22), and so forth.
A further description will be given of the construction and function of each part. The triangular plate 12 folds the web 10 fed through the drag roller 11, in half along the traveling direction, and the web 10 folded in two is fed through the lead-in rollers 13a and 13b. The downstream nipping rollers 14a and 14b nip the web 10 folded in two, convey it while rotating, and press it between them to put a vertical crease in it reliably.
The web cutting unit 20 is used to cut the web 10 folded in two at a predetermined cut-off length position and consists of a saw cylinder 21 and a receiving cylinder 22 rotating in opposite directions. The saw cylinder 21 is provided with a saw-blade holder 24 having saw blades 23 in the outer periphery along the axial direction. The receiving cylinder 22 is provided with a rubber bed 25, made of an elastic body such as rubber, for receiving the saw blades 23.
The saw blades 23 of the saw cylinder 21 and the rubber bed 25 of the receiving cylinder 22 are arranged so that they mesh with each other. By synchronously rotating them in opposite directions, a sheet (folded sheet) 10a is cut off from the fed web 10 by cutting it in the horizontal direction (direction of the width of the web 10). In this example, the saw cylinder 21 is provided with a single saw blade 23 and the receiving cylinder 22 is provided with a single rubber bed 25. Therefore, if each of the cylinders 21, 22 makes one rotation, cutting is performed once.
The accelerating belt conveyor 30 is equipped with a pair of conveyor belts 31, 32 facing each other. Each of the conveyor belts 31, 32 passes around guide rollers 33 and is constructed such that the traveling speed can be arbitrarily varied to some degree. The conveyor belts 31, 32 receive the sheet 10a cut off from the continuous web 10 by the web cutting unit 20 and nip it between them. The moment the sheet 10a is nipped, it is conveyed to the catching-folding unit 40B at the speed corresponding to the speed of the catching-folding unit 40B.
As shown in FIG. 24, the catching-folding unit 40B consists of a catching cylinder 42 equipped with catchers 41, and a folding cylinder 45 equipped with gripper tools (hereinafter referred to simply as grippers) 43 and folding blades 44. The front end of the sheet 10a fed through the conveyor belts 31, 32 is gripped by the grippers 43, and when the sheet 10a is being rotated and transferred, the folding blade 44 of the folding cylinder 45 engages with the catcher 41 of the catching cylinder 42. At the position of the engagement, the sheet 10a transferred to the catcher 41 is folded along a crease perpendicular to the conveying direction.
In the illustrated catching-folding unit 40B, the catching cylinder 42 has two catchers 41 and the folding cylinder 45 has two grippers 43 and two folding blades 44. As a result, two folded sheets 10b are formed in one rotation of each of the cylinders 42, 45.
The paper discharge belt conveyor 46 is constructed such that the folded sheets 10b, formed as described above, are transferred to the subsequent steps, that is, a sheet alignment stacker 80 (see FIG. 22), etc. For instance, as shown in FIG. 22, in the sheet alignment stacker part, the folded sheets 10b may be fed into a stacker (not shown) by transferring them onto a vane wheel 81 and then delivering them onto a paper discharge belt conveyor 82.
In the aforementioned construction, when cutting off a predetermined cut-off length from the printed continuous web 10 by the saw cylinder 21, the predetermined cut-off length C is given asC=Vo/(Nc·n)where Vo is the traveling speed (conveying speed) of the web, Nc is the number of rotations of the saw cylinder, and n is the number of saw blades.
The cut-off sheet 10a is accelerated in one breath from the traveling speed of the web 10 to the speed Vb (i.e., the peripheral speed of the folding cylinder 45) of the catching-folding unit 40B and transferred onto the folding cylinder 45 at the traveling speed Vb.
Subsequently, the sheet 10a fed from the conveyor belts 31, 32 is delivered to the gripper 43 of the folding cylinder 45 and catching and folding are carried out.
A folding machine capable of varying the cut-off length of a web (i.e., a folding machine for a variable cut-off length type rotary printing machine) is disclosed in Patent Document 1 by way of example. This folding machine is provided with a cut-off cylinder, and a delivering cylinder for cutting a ribbon (web) into folded sheets having the desired cut-off length in cooperation with the cut-off cylinder. This delivering cylinder has a cylinder center line and a peripheral surface region. The peripheral surface region of the delivering cylinder has an adjustable diameter portion arranged thereon. This adjustable diameter portion is connected to the delivering cylinder and is movable toward and away from the cylinder center line to adjust the desired cut-off length of a folded sheet. In addition, there is provided a jaw cylinder, which has a cylinder jacket and jaws provided in this cylinder jacket. Furthermore, the peripheral surface region of the delivering cylinder has a pushing blade for folding a folded sheet into the jaws in cooperation with the jaws so that the cut-off length of a web can be varied.
In addition to the catching-folding unit 40B consisting of the catching cylinder 42 equipped with catchers 41 and the folding cylinder 45 equipped with the gripper 43 and folding blades 44 for folding a sheet is a folder, which employs a chopper, such as a chopper folder disclosed in Patent Document 2.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-233545
Patent Document 2: Japanese Patent Publication No. 2532507